I am livid. Absolutely fuming. So angry in fact I swore on the phone to my mom (and I'm not a swearer by nature). 
When we went to the in-laws last weekend SiL and her kids were around. The eldest had been sent home from boarding school with German Measles though "supposedly" (according to her father who is NOT a doctor) not contagious any more. MiL had an email this morning, just before we went to lunch (and then drive home to East Anglia), saying that Niece3 now has the German Measles, too. Which means Toddler and I have been exposed while both nieces were contagious (because you're contagious for a week after the spots DISAPPEAR and Niece1 still had spots when I saw her; you're also contagious for a week before spots appear and it has an incubation period of two weeks). Niece3 (who is 8) in particular was all over Toddler (she loves him to bits) -- was cuddling him, touching him, in his face playing, etc.
This past week I have been to numerous toddler groups/activities, on play dates to the parks and playgrounds, around pregnant friends (one of whom is only about 7 weeks pregnant after years of trying) and babies too young to be immunized. This does not include the hundreds of people we have been in contact with in town, in the shops and cafes, at the wedding on Saturday, etc.
They have brought brand new baby Niece4 (born Friday) home to their house of ill and have invited everyone to her baptism this coming Sunday (bank holiday weekend Sunday). Niece3 broke out in her spots on Friday so will still be contagious. BiL is telling MiL that Niece3 is only contagious 5-7 days so can still go round to hers for Latin lessons on Friday.
I am so (excuse me) fucking pissed off I can't even explain. I now also feel I need to tell my friends who are pregnant and those with babies too young to be immunized that I may have carried this disease to them.